The Cell Cycle Day 3

Cancer: Out of Control Cell Division The defining feature of a cancerous cell is that is divides much more often than is healthy- creating a stack of cells called a tumor How does it do that? It has to bypass all the checkpoints that tell it to stop dividing

The Basics of Cell Division G1: Cell Growth, makes duplicate organelles, increase in size S phase: Duplicates all the chromosomes- photocopying of information G2: More growth, time needed to gain strength for mitosis Mitosis- Cell divides up the chromosomes so each of the new daughter cells has all the information Cytokinesis- The cell breaks into two cells

Key Regulation Points G1 check point before S phase (DNA replication) can start, pass if: – Nutrients sufficient – Growth factors present- there is a need for more cells – Cell is big enough – DNA is undamaged

Key Regulation Points G2 check point before Mitosis – Chromosome replication completed – No DNA damage – Active signals to start mitosis (chemicals in the cytoplasm) Metaphase check point before cell splits – All chromosomes are aligned to be equally passed down to the new cells

Thinking like Cancer Which regulation point(s) would prevent cancerous growth? What are a few ways cancerous cells could bypass those points?

How do checkpoints work? Hypothesis: The cell cycle is directed by specific signaling molecules present in the cytoplasm

How would you design an experiment to test this hypothesis? Materials: – Cells in culture – Any measurement device Think about: What data are relevant? How long will your experiment take?

What do we know so far? Still working out all the chemical and physical signals. Over 50 growth factors have been identified Different cell types respond differently to different growth factors

PDGF

Contact inhibition Normal cells form only a monolayer in culture Why?

Anchorage dependence Normal cells must have a surface on which to grow or a tissue attachment to continue replicating. Why?

Telomeres- fingerprints of cancer Cancer often has specific characteristics related to too much division Each time the cell divides it replicates its chromosomes- increasing the chance for mutation and shortening the telomere (the end of the chromosome)

Discovery of telomerase Telomerase re-lengthens the chromosome to enable division to continue Cancer cells have to increase telomerase activity so that they do not die This is a key regulation step of a cell’s lifespan